Control system



April 7, l1942 A. El MELHosE E+ AL 2,278,460

l{Sheets-Share?. l

mvg

j A ATTORNEY A. E. MELHosE ETAL 2,278,460

April 7, 1942.

CONTROL SYSTEMA Filed Aug. 29, 1940 v 4 Sheets-Sheet 2 April 7, 1942.

A. E.' MELHOSE ET AL CONTROL SYSTEM Filed Aug. 29, 194@ 4 Sheets-Sheet' 3 A. E. MEL H055 /M/EN TORS nl. W rUTH/LL ATTORNEY April 7, 1942. A. E. MELHosE ET AL 2,278,460

CONTROL `SYSTEM `Fi1ed"Aug. 29, 1940 4 sheets-sheet 4 SYLLABIC AMF. D57.' CKT.'

l y' n N f PD AEM-Hose l /M/ENTORS: W W ruTH/LL ATTORNEY Patented Apr. 7, 1942 f *CONTROL SYSTEM Alfred E. Melhose, Westfield, N. J., and Walter W.

Tuthill,

Jackson Heights, N. Y.,

assgnors to Bell Telephone Laboratories,l Incorporated, New York, N. Y.; a corporation of New York 'Application AugustZB, 1940, Serial No. 354,650

6 Clarins. (el. 179-4) This invention relates to communication systems and particularly to switching means in a system wherein a rst typ-e of transmission is interpolated in ak second type of transmission during lullsand pauses in the said secondtype of transmission. i

The object of the invention is to'provide a circuit arrangement for performing kswitching functions to conditiony the transmission channel for one or another type of 4transmission with the utmost speed so as lto prevent interference with such transmission.. Heretofore so-called kick circuits or accelerating circuits have been provided for various purposes but such circuits have usually employed additional apparatus such as condensers, transformers and .'nductances- The present invention makes'use of a novel circuit arrangement of relay windings and com trolled circuits withoutthe usel of other apparatus in additionto 4that employed for the normal use of such relays. In addition, the present invention provides a particularly useful, economical and fast operating relay arrangement employing small and inexpensiverelays.

In a preferredland specic embodiment of the invention herein disclosed by way'of example, 'a so-called interpolated .telegraph and telephone system is provided with a chain ofrrelays known as the transmitting chain, whose dutyy it is to -re spond to voice currents and tocondition the transmission channel for telephone transmission; This chain oi relays must be fast acting and comparatively slow releasing, thislatter .characteristic being obtainedthrough the use of hangover circuits,r The principal hang-over circuit is made to control all the relays in the chain beyond a given point and additional hang-over may be provided at other points along the chain. In the present disclosure there are provided seven relays in av chain, the iirst being known as the transmitting master 'and being responsible for the proper operation ofthe rest each ofwhich has some specic-dutyto perform. The second relay inthe chain'is known --as the Vtransmitting voice hangover relay and itsduty is to prevent the release ofthe'remainder of the chain'for a given-time after the transmitting master has .released. Another'hang-over is provided, as will be apparent from the following description.v

Since all relays of this the utmost speed the remainder of the relays are made dependent for their operation upon themovement of the armature of the master relay from its back contact, thus eliminating 'from their operating time even the travel chain must operate .with

time of the armature of the master. Since the next relay in the chain must remain operated for a given hang-over period after the release of the master its holding circuit, involving the hang-over'circuit must be separate from the fast operating circuit for the remainder of the chain. Therefore the TVI-IO relay operates the rest ofthe chain in a similar manner, that is, by the breaking of a circuit at the back contact and armatureof TVHO. Consequently, special meansN must be provided to make TVI-IO fast operating, and this means is embodied in anaccelerating circuit involving separate windings on the TM (transmitting master) and TVHO relays; This accelerating circuit is rendered,v active as soon as the armature of TM- leaves its back contact andremains active -only until the armature of TVI-IO reaches its front contact. This circuit is also so arranged that it does not become active during the release of these relays, dueto the fact that the armature of TM must reach its back contact again before the armature of TVHO leaves its front Contact. During the time that the said accelerating circuit is active the cores of these two relays are subjected t0 a strong magnetizing circuit which will cause th'em t0 move their armatures speedily. i

A feature of the. invention is a chain of relays uniformly fast operating but slow releasing by different degrees, employing an accelerating circuit to gain the utmost speed in operating and toovercome the delay characteristics introduced by the ,provisions for slow release. n

Another feature is an accelerating circuit for a chain of two relays, responsive to the movement of the armature of the rst relay from its back contact for strongly energizing both said relays until the second of said relays has moved its armature to its `front contact.

Another feature of the invention is an accelerating circuit for a chain'of two relays effective only during the movement of the-armatures of said relays from theirback to their front contacts. Still another feature of the invention is a drain of two relays, the rst of which is free to respond without delay to energizing impulses and the second of which is delayed by a hang-over circuit in its release and which `relays control a self-energizingfcircuit only during the forward movement of their armatures. f This invention is an improvement in the system disclosedv in Patent 2,207,720, granted to Cole' etal., July 16, 1940. 'I l The drawings consist lofffour Vsheets or circuit Fig. 2, partly schematic and partly circuit dia- `y gram, shows the telephone and controlling circuits;

Fig. 3 shows the receiving telegraph circuits;

Fig. 4 is a detailed circuit diagram of a syllabic amplier-detector circuit indicated by the rectangle 2 I3 in Fig. 2 and intended to be fitted into the general diagram of Fig. 2 at the broken lines X-X, Y-Y and Z-Z.

One terminal of a system is shown but it will be understood that at some distant point a similar terminal is located so that speech coming in over channel will be transmitted from the radio transmitter 202 and its antenna 203 to be received at the said distant point over the antenna 204 and the radio receiver 205 for transmission into the speech path at that point corresponding to the channel 20|.

While speech is being transmitted from channel 20| over the antenna 203, the telegraph transmitting apparatus of Fig. 1 is inactive and the telegraph receiving apparatus of Fig. 3 at the distant point is similarly inactive. By the same token, the telegraph transmitting apparatus of Fig. 1 at the distant point and the telegraph receiving apparatus of Fig. 3 at the near end, as shown, will be in operation.

In general, speech over channel 20| enters the hybrid coil 205 provided with the usual balancing network 201, passesover path 200 through the network 209 to the voice operated gain adjusting device (termed vogad for short) 2| From the vogad 2|| speech currents enter the hybrid coil 2| 2 where they split, part going on to the main speech channel and part entering the syllabic amplifier-detector 2|3 for control purposes. The output of the amplifier-detector 2|3 operates the transmitting relay chain 2| 4 which performs a variety of switching functions, as will be more clearly set forth hereinafter. At present it is suicient to say that the transmitting chain 2|4 clears the way for the speech currents to the antenna 2|3 and that the distant receiving terminal similarly conditions the receiving circuits thereat for the proper reception of the speech currents. The main portion of the speech currents then pass from the hybrid coil 2| 2 into the delay circuit 2 I5, through a repeater 2|6, and the first transmitting suppressor 2|1. Thereafter the speech path is through privacy circuit 2| 8, the second transmitting suppressor 2|9, and another part of the privacy circuit 220 to the hybrid coil 22|. Speech currents then pass to the hybrid coil 2 22, thence to the transmitting repeater 223 to the radio transmitter 202.

At the distant receiving end the speech currents transmitted from the radio receiver pass through the receiving repeater 224 into the hybrid coil 225. At this point the control tone which accompanies speech is diverted to the control tone filter 223, to the receiving detector 221, which operates the receiving relay chain 228. This receiving chain responds to the control tone transmitted from the distant end through the operation of the transmitting chain 2|4 thereat and, like the transmitting chain, performs a variety of switching functions which will be more fully described hereinafter. At present it is sufficient to say that the receiving chain clears the way for the speech currents to reach the hybrid coil 206 and channel 20| The speech currents leaving the hybrid coil 225 enter the next hybrid coil 229 and thence pass through a part of the privacy circuit 230, the first receiving suppressor 23|, another part of the privacy circuit 232 to the second receiving suppressor 233. From this point the speech currents pass through the variable suppressor 234, a low-pass ilter 235, a volume controller 236, a repeater 231, a network 238, and thence to the hybrid coil 206 from which they pass over the channel such as 20| at the said distant terminal.

The functions of these various pieces of apparatus are briefly as follows.

Referring to the details of the speech control circuits, the hybrid coil 206 receives voice currents from the channel 20| and transmits them out over the channel 208. The hybrid coil 206 also receives voice currents from channel 239 and transmits them out over channel 20|. Actually, the voice currents split equally to paths 208 and 239 but are prevented from passing over 239 beyond the repeater 231 by the unidirectional characteristics of this repeater. The function of the balancing network 201 is well known. In this connection it should also be noted that each of the hybrid coils 2|2, 22|, 222, 225 and 229 are provided with appropriate balancing networks. The networks 209 and 238 are provided to perform certain functions necessary in commercial telephone circuits to compensate for the differences in transmission when the channel 20| is connected to different types of telephone circuits. They play no particular part in the present invention as their adjusting circuits are not shown but they are included in the schematic part of this diagram in order to render the diagram as complete as possible. The vogad 2| is a means for adjusting the gain applied to the voice currents incoming thereto so as to provide a uniform level at the point of its output. The coil 2|2 allows a small part of the voice currents to be taken off to the syllabic amplifier-detector 2| 3. The delay circuit 2|5 is an arrangement by which voicecurrents are delayed to allow time for the transmitting chain 2|4 to properly perform its functions before the voice currents are nally delivered to the antenna 203. Since these delay circuits entail certain loss in transmission, amplifying means are associated therewith in the form of a repeater 2 E which is shown as a one-way amplifying repeater. The first transmitting suppressor 2|1 and the second transmitting suppressor 2|9 both act to block speech currents therethrough when the relays of the transmitting chain 2|4 are in the position shown. When, however, the transmitting chain is operated both transmitting suppressor 2 |1 and transmitting suppressor 2|9 give a clear path for the transmission of voice currents. The two privacy system units 2|8 and 220 are included to render the speech modulated wavesbetween the antenna 203 and the distant antenna 204 unintelligible to simple detection receivers but do not form any essential part of the present invention, being included for the purpose of rendering the schematic layout as complete as possible. The function of the hybrid coil 22| is to transmit to the hybrid coil 222 either speech coming from the privacy system unit 220 or telegraph signals coming from Fig. l, above. The function of the hybrid coil 222 is to pass on to the transmitting repeater 223 both the output of the hybrid-coil 22| and the control tone originating from the oscillator 240. This oscillator is a out disturbingr the voice currentsenteringfthe receiving circuit thereat. Y I A Current from the oscil1ator240 enters the control tone enabler24l,` which is-under control-"oi the transmitting chain 214, as will appear hereinafter. Whenthe voicel takes command'7of-the transmitting chain 2 I 4 'fand certain relays in ythe telegraph a transmitting A'apparatus of 1 are properly operated, the controltorie enabler v2M will allow alternating current vfrom fthe Ylstmrce 240 to enter the control tone compressor 242 and from this pointlthe control tone vvs`1illbe'-pas`sed through the lter 243 to thefhyb'ridfcoil 2722. The effect, therefore; vis that'lwhen' lthevo'ice' takes command of the transmitting chain'2l4, control -tonel at-fullvolume willlbe delivered to the hybrid coil 222. A short time"thereaft er-,`"as measured by the delay circuit `-2l5fandcontrolled by a connection inthe voice path'- between the rst transmitting suppressor2l1 and the i'lrst unit of the privacy system "-2'8,5` tl'iecontrol'f tone compressor will lperateto regulate the volume of the control tone being"` delivered to'f'the hybridcoil 222. v f l The transmitting repeater 223'is a Well-known type of one-Way amplifier. The 'radiotransmit-4 ter 202 and its associated"antenna'203`need'no special description. Likewise, the radio' receiver 205 and its associated'antenna204 needno special description. The repeater '224fis,' like the repeaters 2I6 and 223,' a one-way 4vamplifying' device. v lf .I

The hybrid coilv 229receivesgtheoutputofthe radio receiver '203- andy allows part vof this"out-a'J 'putte QW-to 'tlljcltloltone flter`226 Which delivers to'the receiving detector221'only'-the 'f The' hybrid e611 V225 also delivers control tonel to the next hybrid coil' 229 thespeech currents; the accompanying control tone being `i'lltered out later. Hybrid coil 229 acts to deliver the speech currents which are transmitted from lthe radio receiver 205 to the privacy system unit 230 and the various circuitv units thereafter. ing intervals of telegraph transmission the hye brid coil 229 delivers the output of the radio re-Jy ceiver 205 to the telegraph receiving 'apparatus of Fig. 3. Y.

The privacy systemvunits 230 and A232 used to insure a degree of secrecy are used incomplement with units 220 and 218 in the transmission of intelligence by translating fori delivery to channel 20| the otherwise unintelligibleitrans# mission from the anterina203y lto. the'antenna 204. The iirst receiving suppressor '23Ifv andthe second receiving suppressor 233,` b'oth under com trol of the receiving chain 22,8,"operate'-td'block the speech pathV during -those 'intervals when `the control tone is `absent from'thefA `tnansmission being received by the receiver 205, :When con# trol 'tone is present as Aan. indication thatA speech` is present, the ecei'virg'-hatin 228-takes the sitionv shownby the lvarius relays and the re"' ceiving Suppressors' 23| and v'233l Y"give a'fclear path for speech currents toward the hybrid:y coil 206 and the channel`20l. lThe variable suppresfv sor 234 is a device used to causethe transition from speech to silence and from silence to speech to be slow so that static and other extraneous noises will not be applied to and'removed from the speech circuit abruptly and so 'disturb the listener. The low-passiilter 235 effectuallyk blocks any control tone which may have accompanied 'peech''to thisn point -zyr'idf'allowsv only the speech t0 go into the volume controller 236. l f Atv this point it should -b'ev noted that between thelow-'pass filter 235 and the volume controller 236 there is' afconnection' to the receiving `detector`221. Thus when the' voice takes command atY they distant' transmitting end; control tone from the oscillator 240 is transmitted by the radio transmitter at full volumefandthis will enter'thefcontrol tonelter 226 and the receiving detector 221 tov insure the propenoperationfof thef receiving masterrelay Within the receiving chain 1228.' "-Bytheitime fthat the voice arrives, the receiving Ichain "will 'have' "conditioned" the receiving circuit, particularly 'by operating the rst and secondreceiving'Suppressors231 and 233 and the variable suppressor 234. VAsthe control tone' isr'educ'ed 'in vvolume through the Aaction of the control tone 'compressor- 242 or throughselective' fading in the radiopath.'y voice currents from the iconnection between 'fthe lowp'ass =lter235 and the volume controll'era'236 will vreach*-therec'eivi'ng'- detector `221 lto augment the operatin-of this device and insure the'proper vand continuous operation of the receiving chain even during' periods when fading or 'other vdisturbances'in the' mutable link cause the received control tone to drop to a value where'the` continued operation of be unsatisfactory; f" y a `"I'hwat part of 'the circuit between and including radidtransmi'tter 202|' and radio receiverl 205 is spoken of i-asamutable link since it comprises asignaling .channel capableof or liable to change from internal orlkeiternalwcause which may. give rise to interfering, energrfor.. moreispeccauy.

' wand.ading'prphange of'wattenl Itis t0' beunderstoo'dfhoweventhat the present Showingl lis by, way ,ofexam'ple 'and that the .termy i jfmutablev link. does Vnot necessar ily meanjthat a space'radio link isinvariably involved butl that theterm is, broader in its meaningvjand "includes, any `channel liable to changeA from internal or external cause.`

Thevolume controller 230 is a device generally under theI supervision of a technical operator for controlling. the volume of speech deliveredfto 20| as indicated by-a .monitoring device1 not shown, connected between this unitv and the receiving repeater 231. Thereceivingrepeater 231 is; likejthe other repeaters 210, -223 andg224; a one-way amplifying device. f Y V; The syllabic ampliiler-detectorv2l3 is a device which `will be more fully `described hereinafter. Itjisconnectedto the hybrid coil2l2 through the broken-line: Z-'Z and delivers its output through the lbroken 'lineX-X to the' transmitbetween v`oice"curren'ts""and fortuitous' ldisturbv ances so that the transmitting relay chain 2|4 will not be unnecessarily'operated by such fortuitous disturbances. Further description of this ampliiier-'detector will be found hereinafter. At present' it is xonly 'necessary vto point out that voice currents'coming-'in'to the Ahybridfcoil 212 the receiving chainmight will cause the amplifier-detector 2|3 to .operate the transmitting chain2l4.

The transmitting chain comprises a transmitting master relay 250 and a' chain .of relays 25|, 252, 253, 254, 255 and 256. The transmitting master relay 256 responds directly to the ampliiler-detector 2|3. The relays 250 and 25| together provide an accelerating circuit for the -sure and speedy operation of the remainder of the chain of relays. It will be noted -that lthe lower windings of both relays 250 and 25| are included in a series circuit which extends from ground connected also to the armature of v relay 25|] through the lower windings of relays 250 and 25| and thence to a resistance 258 and battery. However, the connection between the lower winding of relay 25| andthe resistance 258 extends to the back contact of relay 25,0 which, as `before stated, is connected to ground. When relay 250 operates,then at the instant that the armatract their armatures strongly and with the ut` most speed. When relay 25| moves its armature into connection with its front contact, the two lower windings of these relays are mutually connected in a closed circuit but the relay 250 will have moved its armature to its front contact and relay 25| will have become fully operated. VRelay 25 |V is now held operated in a circuit from ground, the armature and iront contact of relay 250, re-

sistance 259, resistance 260, the upper winding of `relay 25|, resistance 26| to battery.

It should be noted that when underinfluenceof the amplifier-detector 213 the-transmitting master relay 250 becomes deenergized, the armature of relay 250 will reach its back Contact and establish the original circuit for shunting the two lower windings of relays 250 and 25| before relay 25| can release its armature. Relay 25| is known asthe transmittingvoice hang-over relay and through the operation of the circuit including condenser 262 and resistance 260 this relay is caused to hold its armature operated until condenser 262 can become sulciently charged. By the proper selection of the values of resistance 260 and condenser 262., the hang-over period by which the release of relay 25| vis delayed beyond the release of relay 256, may be adjusted to any desired value.

Thus the accelerating circuit operates only on the forward operation of these relays 256 and 25| and plays no part in the release thereof.

The operation of relay 25| causes the operation of relays 252 to 256, inclusive. Relay 252 to 255, inclusive, have their windingsin a series circuit extending to the back contact and armature of relay 25| and from this point extending also through resistance 263 to battery. Since the armature of relay 25| is grounded, the circuit through the windings of relays 252 to 255 normally is shunted. However, as soon as the relay 25| moves its armature from its back contact, the circuit through the resistance 263 will become eiective and relays 252 to 255 will immediately become operated. Through the operation of relay 255, relay 256 is operated.

Relay 252 in its normal position affects the rst transmitting suppressor 2|1 to block Voice currents delivered to it by the repeater 2 I6. Upon its operation, however, relay 252 changes this condition so that the rst transmitting suppressor 2|,1 now enables the free transmission of voice currents, Relay 253 is the privacy relay and ,this causes certain switching functions to take Aplace when speech is to be transmitted out over antenna 203. The privacy relay 253 also functions on its front contact to operate the transmitting signal relay 264 and thus the signal lamp 265 to indicate that the transmitting chain is in operation.v The relay 254 controls the second transmitting suppressor 2|9 and relay 255 functions tocause the operation of the transmitting telegraph enabler relay 256. This relay is provided with a hang-over circuit comprising the resistances 266 and 261 and the condenser 268 so that thetransmitting telegraph enabler relay does not become released for a given period after the remainder -of thel transmitting Chain has released.

It has been noted brieiiy hereinbefore that the receiving detector 221 is first operated by control tone through the lter 226 at comparatively high volume and later, after the receiving chain .228 has operated, is then controlled by both the control tone at lower volume through the iilter 226 and by voice currents coming in over a connection between the low-pass lter 235 and the volume controller 236. The receiving detector normally holds the control master relay 210 operated and when the receiving detector responds to these incoming control tone and-voice currents, it allows relay 210 to become deenergized. During the normal condition, then, relay 210 is operated and the chain of relays controlled thereby is in the position shown. Upon the release of relay 210 a circuit is completed from ground, the armature and back contact of master relay 210, resistance 21|', resistance 212, the windings of relays 213, 214 and 215 in series, and resistance 251 to battery. Upon the operation of relay 215 a connection is established from ground, armature and front contact of relay 215, resistances `28| and 282 and thence through the windings of -relays 216, 211, 218 and 219 in series to battery. Resistances 21| and 212 of the condenser `28|) from a hang-over circuit so that it is not for a given period after the master relay 210 has again operated that relays 213 to 219, inclusive, may release their armatures. In addition, the resistances 28|, 262 and the condenser 283 from a hang-over circuit for relays 216 to 219, inclusive, so that it is not for an additional period after relays 213 to 215 have released that relays 216 to 219 will release.

Relay 213known as the receiving suppressor relay, in releasing changes lthe circuits of the variable suppressor 234 so as to allow what may be termed a gradual closing of the voice path. Thereafter, in a time interval as measured `by the hang-over circuit of resistances 28| and 282, and condenser 283, the rreceiving suppressor relays 216 and 219 will cause the rst and second receiving Suppressors 23| and 233, respectively, to fully close the voice channel leading to the `hybrid coil 206. It should be noted that the action in the opposite direction, that is when the master relay 210 releases and the relays of the chain operate, is to quickly remove the blocking action of suppressors 23| and 233 and then to gradually and fully open up the voice path through the operation of the variable suppressor 234. The telegrad relay 214 operates to control the telegrad of Fig. 3. Relay 215, known as the receiving printing master relay, controls the printer circuit in Fig. .3. The receivingA echo hang-over relay 21| controls the amplifier-detector v2.13 at the same terminal and the vogad disabler relay 218 controls the vogad 2|I so that while speech is being received at the transmitting terminal, the gain of the vogad 2 I I will remain unchanged. Relay 219 when released causes the operation of. relay 284 and in turn the glowing of lamp 285, as a signal that the receiving chain is effectively operated. i l

The transmitting amplifier-detector 2 I3 shown in full in Fig. 4 is -designed to beunoperated by the maximum noise which may be expected on the transmitting circuit but to be operated quickly by speed signals of both high and low amplitudes. Features of this amplifier-detector to be described below provide added discrimination between speech and line noise, and the reduction in false operation afforded by this protection en;- ables improved operation to be attainedfor the case in which noisy telephone linesvareconneoted to the terminal. l Y,

The amplifier-detector 2|3 comprisesV a voltage amplifier-detector 400 forwcontrollingythe operation of the transmitting chain 2I4v and a syllabic type amplifier-detector 40|, operating as an enabler for the voltage amplifier-detector 400, the two amplifier-detectors 400 and 40| being coupled to the common input circuitV from the hybrid` coil 2I2 through van input transform'- er 402, the primary winding of which is shunted by the terminating resistance 403 and the secf Y ondary winding of which is shunted byva condenser 404. A portion of the secondary winding of input transformer 402 is shunted by a resistance comprising the three sections 405,A 406 vand 401 arranged as a Voltage divider.

The voltage-operated amplifier-detector 400 comprises one `stage of alternating current amplification consisting of .a single pentode vacuum tube 408 having its cathode connected to thelower terminal of the secondary winding of input transformer 402 and the lower terminal of the voltage divider comprising resistances 405, 406 and 401, and its control grid connected to the tap of the voltage divider betweenz the resistances 405 and 400. An interstage transformer `400 is provided Vwith a primary Winding connected in the plate-cathode circuit of tube 408 and a secondary winding tuned to 1300 cycles by the conf denser 4|0. A rectifier consisting of copper-oxide rectifier units 4| and 4 I2 and condensers 4| 3 and 4I4 has its input connectedv to the secondary of transformer 409 and resistance 4| 3. A stage of direct current amplification consisting of a single pentode vacuum tube 4I6 is provided with its control grid-cathode circuit connected tothe output of the rectifier .across shunt resistance 4I1. The master transmitting relay 250 which controls the operation of the transmitting chain of switching relays 25| to 256, inclusive, has its operating winding connected in the plate-cathode circuit of the amplifying tube 4 I 6.

The syllabic amplifier-detector 40| comprises a stage of alternating current amplification consisting of the single pentode amplifying vacuum tube 420 having its control grid-cathode circuit connected to the terminals of the secondary winding of input transformer 402. An interstage transformer 42| is provided with a primary winding shunted by resistance 4 22 connected in the plate-'cathode circuit of tube 420 and a secondary winding which istunedto 1800 cyclesvby the shunt condenser 423.A A rectifier is provided by the diode portionof the diode-triode vacuum tube 424 connected to the secondarywinding of'tr'ansformer 42| through series condenser 425. Aband-r pass filter for passing frequenciesbetween 1 an 15 cycles consists of resistances 426 to 430, in- I tube 424 has its control grid-cathode circuit connected to the output of this lter. Relays 435 and 436 have their operating.y windings connected in series in the plate-cathode circuit of the amplier portion of tube 424.

The various plate, screen and grid filters and bias circuits shown are necessary for the successful operation of the amplifier-detectors 400 and 40|. Tube 420 obtains its grid bias by cathode voltage drop through the retardationl coil 431 which also provides series feedback. The tube 424 obtains its grid bias by -cathode voltage drop through the resistances v438 and 439. The con- Adenser 440 operates as the'plate lter for tube 424. 4The tube 408 obtains its grid bias by cathodevoltage drop through the retardation coil 44| which also provides series feedback and the associated condenser and resistance provide the screen filter for the same tubeL TheY tube 4|6 obtains its 'grid bias from the filament battery by Vmeans of thek voltagedivider consisting of resistances 442 and443. i K y I In the unoperated condition of relays 435 and 430, that is, with no lspeech Waves being applied to the input of amplifier-detector 2|3` through input transformer 402, the lower resistance por- ,tion of the voltage divider comprising resistances .405 to 401 is short-circuited throughy the normally closed contacts ofthese relays in series,l

so that the voltageinput tothe amplifying tube 408 is decreased by about l0 decibels. Ihis reduction in sensitivity is sufficient to prevent false operation of the voltage amplifier-detector 400 in Aresponse to any normal amount of line noise from the transmitting circuit which may be impressed on its input through the input transformer 402. The line noise will be prevented from causing false operation of the syllabic amplifier-detector 40| by the band-'pass filter connected lbetween the secondary of transformer 42| and the' tube 424 which will transmit only the syllabic frequencies of .speech and will'no'trtransmit the relatively steady noise.

Now letit be assumed that speech signals from a subscriber connected to channel 20| are lbeing transmitted out toward thefantenna 203. A portion of 'the speech signals will be ldiv-erted into the device of Fig. 4 "and will be impressed, along with thenoise waves received, on the input of the transmitting amplifier-detector through input transformer 482-and will be divided between the syllabic amplifier-detector 40| and the voltage amplifier-detector 400. f l The portion of the speech signals and noise entering the syllabic amplifier-,detector 40| will pass through the inters'tage transformer 42|, Whichbeing tuned to 1800 cycles, will pass most ofthe higher voice frequencies (1500 to .3000 cycles). YIt has been found thatifor consonants in speech a better signal-to-noise ratio is obvtained in the region of 1800 cycles and that words'` beginning or endingv in consonants are the most susceptible tomclipping. The tuning of the syllabic amplifier-detector 40|: to 1800 cycles, as described, effectively makes this amplifier-detector a consonant-operated enabler device and providesl improved loperation, of thev transmitting chain 2|4. Y

The wave passed thetuned transformer 42 Ir are transmitted through the series condenser 425 to the diode-detector portion of the tube 424 which operates todemodulate the speech frequencies and to produce all the low frequencies' caused by the syllabic nature of the speech, these products appearing across condenser 425. Those of the demodulatedproducts which are between 1 and 15 cycles pass through' the band-pass iilter and are then amplified by the amplifying triode portion of the tube 424.

The ampliiied waves inthe plate-cathode circuit of the trode portion of the tube 424 pass through the operating windings of relays 435 and 436 in series. These relays are poled and biased differently so thatthe relay 430 operates at the beginning of a Word or syllable and relay 435 operatesratv the end of a word orr syllable if the speech amplitude is sufficient. The result of operation of either of these relays is to remove the short circuit from about resistance 401,

thereby increasing the voltage input to the amplifying tube 408 in the voltage amplier-detector 400 by about 10 decibels and thus effectively increasing its sensitivity by that amount.

The speech and line noise impressed on the input of the amplifying tube 408 are amplified thereby and passed through the interstage transformer 438. This transformer being tuned to 1300 cycles, will be particularly efective in transmitting lthe lower speech frequencies (800 to 1500 cycles) and in this frequency range a better signal-to-noise ratio is obtained for the vowels in speech. The tuning of the circuit in this manner therefore makesl the voltage amplifier-detector 400 eifectively a vowel-operated device.

The waves passed by interstage transformer 409 are rectified in the rectier connected between the secondary of transformer 409 and the tube 4|6 and the rectified voltages are applied across resistance 4|1 to the control grid-cathode circuit of the direct current amplifying tube 4|6 which is normally biased by the biasing circuit shown, to approximately cut-oir. This normal bias is overcome by the opposing rectied voltage Relay 211 in the receiving chain operates to disable this syllabic ampliiier-detector. When the chain is in its unoperated position, as shown, so that speech coming in over channel 20| may effectively operate the transmitting chain 2|4, the contacts of relay 211 are closed and thus a battery connection to the plate of tube 4|'6 is completed. When, however, speech is corning in over the radio receiver 205 and the receiving chain 228 is operated, then the consequent operation of relay 211 opens the battery connection to the plate of tube 4|6'and the syllabic amplifierdetector is thus effectively disabled.

Whenthe transmitting chain 2|4'is in its unoperated condition, as shown, then the telegraph i transmitting apparatus of Fig. 1 is rendered ef,

fective; The control circuit comprises a conductor leading fromthe front contact of` both the transmitting telegraph enabler relay 2560 and the iirst transmitting suppressor relay 252. This conductor may be tracedl to the back contact of relay |00, thence through the armature of this relay, resistance |0| and the windings of relays |02 and H13-in series to battery. Thus with the transmitting chain 2|4 in the condition shown, relays |02 and |03 will be unoperated and. the transmitting telegraph apparatus will be conditioned for operation. It should also be noted that at this time a connection maybe traced from ground, the armature and back contact of relay 254, through the armature and back contact of relay |04 for controlling the control tone enabler 24|. Thus when the transmitting chain 2|4 is operated relays |02 and |03 will become operated and render the telegraph transmitting apparatus ineiective andv at the same time the circuit for controlling the control tone enabler 24| will be interrupted and control tone path will be effectively opened up for transmission of control tone from the oscillator 2240i to the hybrid coil/222.

The transmitting telegraphv apparatus consists, generally, of a pair of tape transrnittersflll` and |06; Each of these transmitters has a series of've contacts operating between a spacing battery lead |01 and a marking' battery lead |08 and affecting, in turn, the segments to |20, inclusive, of the multiplex' distributor. This latter piece of apparatus consists, in general, of a motor and synchronizing equipment |I0' operating a shaft |09. This shaft has upon it a number of brushes |2|, |22, |23 andl24. The brush |2| as it passes successivelyl over the segments to |20, inclusive, connectsY these segments to the ring |25 which is connected througheither the armature and back contact of relay |26 or the armature and back contact of/relay |21, thence through the back contact and armature ofrelay |03 and the winding of'y the telegraph transmitting line relay |28 to a point on av potentiometer consisting of the resistances |29 and |30 whereby the relay` |28 will respondA to either marking or spacing potential and thus operate its armature accordingly. When relay |28` is operated by a spacing' signal it closes a circuit through its armature and contact to render the telegraph tone enabler |3| ineffective to transmit telegraph tone from the source |32 to the hybrid coil 22|. When the relay |28 is operated by a marking signal it opens this circuit which aiects the telegraph tone enabler |3| in such a way that alternating current from the source |32 freely passes to the hybrid coil 22| and thence out over the radiotransmitter 202.

It should be noted that when the transmitting chain 2|4 is operated' and, consequently, relay |03 is operated, that a connection is extended from spacing battery lead |01 through the front contact and armature'of relay |03 to the Winding of relay |28 to holdthis relay spacing and, therefore, continuously'to block the transmission of telegraph tone from the source |32 to the hybrid coil 22| The function of brush |22 is as follows: If'the transmitting chain operates at anytime before brush |22 comes in' contact with segmenty |33 or segment |34, then relays |02 and |03 willbe properly operatedv and further transmission of telegraph signals interrupted and the'stepping of the taper magnet prevented. If, however, the operation of the transmitting,l chainv 2|4Y occurs while brush |22'is on either of these segments |33 or |34, a connection will be vvextended from battery, ring. |35N over brush I 22 tor segment |33 andthence vthrough` the windings'of relays |04 and |00, the back contact and armature of relay |02 to ground. This causes the `circuit for the operation of relays |02 and |03 to be opened to prevent the disabling of the telegraph apparatus for this very short interval. This arrangement is provided so that if the voice takes command of the circuit at or during the transmission of the last pulse of a telegraph code, this last pulse may be allowed to be transmitted without interruption.

The function of brush |23 is as follows: The segments and rings of this multiplex distributor are developed for the sake of clarity and the brush |23, now moving downwardly, has reached the point where transmission of the signals from the tape transmitter |06 has been completed. Brush |23 now establishes a connection from ground, ring |36, brush |23,.segment |31, back contact and outer right-hand armature of relay |38, winding of stepping magnet |39, right-hand contact and armature of relay |40 to battery. If relay |40 is on its right-hand'contact, as it should be while this apparatus is operating normally, and there is a sufcient supply of tape for use by the transmitter |06, then the magnet |39 will operate and advance the tape to the nextpunched character. As brush |23 advances it next comes into contact with segment |4| where a connection is established from ground, ring |36, brush |23, segment |4|, the contacts of the taut tape switch |42, which will be closed as long as there is sufficient tape in this transmitter, to the left-l hand winding of relay |38. This connectionialso extends in parallel through the normal contacts and the inner right-hand armature of relay |38 f through the right-hand winding of this relay, and these windings being opposed no operation of the relay |38 will occur. If, however, upon the operation of magnet |39 the taut tape switchV |42 had operated, then only the right-hand winding of relay |38 would have been energized and this relay would then have operated and locked through its inner right-hand armature to ground. This condition would have persisted until the taut tape switch |42 closed its contacts again and brush |23. made contact with segment |4| whereupon the relay |38 would have been automatically released.

During the time that relay |38 is operated each of the segments ||6 to |20, inclusive, would have been connected through the front contacts and left-hand armatures lof relay |38 to marking battery, so that a signal consisting of five marking pulses would have been repeatedly sent each time the brush |25 passed over the segments ||6 to |20, inclusive.

When brush |23 advances to segment |43 a connection is momentarily established from ground, ring |36, brush |23, segment |43, the lower winding of relay |40 to battery. This tends to drive relay |40 to its right-*hand contact where it will remain unless some other circuit is closed to change this condition.

As brush |23 advances further it first causes the operation of stepping magnet |44 in a similar manner to the operation of stepping magnet |39 and attempts to operate the relay |45 and finally closes a circuit to drive relay |46 to its right-hand armature.

The function of brush |24 is as follows: If during the time that brush |24 is on segment |41 relay |02 becomes operated then a circuit will be established from ground, the armature and front contact of relay |02, ring |48, brush |24, segment |41, the upper winding ofrelay |46 75 to battery. Relay |46 will thereupon bedrven to its left-hand contact where it will remain until brush |23 drives it back to its left-hand contact. During the time that relay |46 is on its left-hand contact it will cause the operation of relay |26 in an obvious circuit and thereby initiate'the opening of the transmitting circuit which operates the telegraph transmitting relay |28. When brush |24 reaches the lower segment |49 it will cause the relay |40 to move to its left-hand contact whereupon the relay |21 will be operated and complete the opening of the circuit for relay |28. Itwill be noted that each of these relays |46 and |40 will` be periodically returned to its L right-hand contact at the ending of the period of activity of the other circuit, but if the telegraph transmitting apparatus is now rendered ineffective the relay will return to its left-hand contact immediately thereafter and before any signals can beeffectively transmitted. It should be noted before leaving the description of the transmitting telegraph apparatus that if both the taut tape switches open the left-hand windings of relays |38 and |45, respectively, that the contacts and the left-hand armatures of relay |45 are connected to spacing battery so that rst a series of five marking impulses and later a series of five spacing impulses will be transmitted. This provides .for an occasional transition between a spacing and a marking impulse for the purpose of correcting the distributor speed at the distant end.

When the receiving chain is in the position shown then the telegrad `relay 214 will close a contact on a pair` of conductors leading into the telegrad 300. This will render the telegrad effectiveto operate the receiving telegraph apparatus.A At this time telegraph signals being received by the radio receiver are passed into hybrid coil 229 and thencey into the band-pass filter 30| from which they are delivered to the telegrad 300. 'I'his results in the operation of relays 3,02, 303, and 304 to their marking contacts for each marking impulse delivered to the telegrad 300. Relay 302 is known as the receiving telegraph line relay and for each marking impulse it establishes a ground connection to the ring 305. Relay 304'- is known as the corrector relay. Upon each spacing impulse this relay will cause its condenser 306 to be energized and upon each markingvimpulse this relay will deliver the condenser discharge into ring 301. Relay 303 is known as the auxiliaryrelay and operates on each markingv impulse to drive either relay 308 or relay 309 -to its left-hand contact, respectively.

The receiving telegraph apparatus consists, generally, of two printers 3|0 and 3||` and a multiplex distributor comprising a motor and certain synchronous, equipment 3|2 operating a shaft 3|3 carrying brushes 3|4, 3|5, 3|6 and 3|1. As brush 3|4 moves downwardly it connects the ring 305 through segments 3|8, 3|9, 320, 32| and322 to the selecting magnets of `printer 3|| and thereafter through segments 323, 324, 325, 328 and 321 to the selecting magnets of printer 3|0. Thus for each marking impulseone of the selecting magnets of printer 3|| or printer 3|0 is operated.

` Brush 3|6 i'n moving downwardly makes contact with segments 328 and then 329 while brush 3|4 is traversing the connections to the selecting magnets of printer 3||. The segments 328 and 329 are associated with printer 3|0. The connection t0 segment 328 establishes a circuit .from ground, ring 330, brush 3|6, segment 328,

armature and Contact of relay 308 to the printing magnet 33|. Thus the selection set upon printer 3H) is rendered effective by the printing magnet 33| after the brush 3|4 has completely traversed the segments 323 to 321 and is now engaged in passing over the segments 3|B to 322. As the brush 3|3 advances it makes a connection from ground to segment 329, which leads to the lower right-hand set of contacts of key 332, for purposes which will be hereinafter described.

As brush 3| 6 next traverses segment 333 the printing magnet 334 will be operated.

Brush 3|? makes contact from the ring 335 to the segment 336 during the time that the brush 3H is traversing the segments associated with the printer 3| This circuit from ring 335 extends a battery connection to the two windings of the relay 339 through the rectiers 331 and 338. is now properly in operative condition there will be an open connection 4to the upper winding of this relay at the armature and contact of relay 339. Any marking impulse coming in at this time will be rendered effective by the auxiliary relay 303 to keep relay 303 on its left-hand contact and thus render the printing magnet effective. If, on the other hand, the receiving chain 223 is operated by voice currents then relay 339 which will be released and ground on the armature of relay 33S will cause relay 309 to be driven to its other position where the circuit for printing magnet 334 is opened. Similar action of relay 308 will take place when the brush 3|1 traverses the segment; 34|.

It will also be noted that when the relay 339 is operated, as when the receiving chain 228 is in the position shown, thus denoting the fact that the receiving telegraph apparatus is effestive, that relay 340 will be operated. Relay 340 plays a particular role with relation to the key 332.

Ii" the distant transmitter corresponding to transmitter |96 operates its taut tape switch so as to send out a series of five marking im- .y

noying to the operator then the key 332 may be moved to its right-hand position. Thereupon a circuit will be established from battery, the upper right-hand contacts of key 332, the winding of relay 342, the lower right-hand contacts of key 332 to the segment 329 and when brush 3|6 makes contact with segment 329 a connection is extended to ground on ring 330. This causes relay 342 to operate and this relay locks up and operates to battery on its inner right-hand armature. Relay 342 is sufficiently slow in releasing so that it will remain locked up in a manner now to be described. Upon the first operation of relay 342 a circuit for the operation of relay 343 is closed at the front contact and outer right-hand armature of relay 342. This relay now disconnects the segments 323 to 321, inclusive, from the selecting magnets of the printer 3m and extends them to conductor 344 which, with the left-hand contacts of key 332 in their normal position, extends the ground connection each time the brush 3M connects with a segment 323 to 321. inclusive, to the winding of relay 342 to maintain this relay operated.

If at the distant end the taut tape switch should return to normal then ground impulses If this telegraph receiving apparatus will not be supplied to the winding of relay 3132 at sufficient intervals to keep this relay operated and it will therefore release and by releasing cause relay 343v to return to normal, so that the printer 3| again becomes effective. If during the time that relay 342 is locked up the receiving telegraph apparatus is rendered ineffestive by the operation of the receiving chain 228, then relay 34|! returns to normal and this maintains relay 342 locked up until the telegraph apparatus is again rendered effective through the operation of the receiving chain 228.

Te relay 342 may be unlocked at any time by moving the key 332 to its left-hand position.

As brush 3 5 moves it alternatively makes contact with segments connected to either conductor 345 or 346. These conductors are connected to diierentA windings of the corrector relay 341 and therefore the discharge of the condenser 336 will tend to operate the relay 341 in one direction if the motor 3| 2 is running fast or operate the relay 341 in the other direction if the motor 3|2 is running slow. The correcting means is well known and will not be further described except to note that a device 348, which will indicate fast or slow operation, is inserted at this point tov indicate that correction may be properly made.

What is claimed is:

1. In a communication system, a transmission channel, means for normally connecting a means for transmitting `a first type of signals over said channel, means for alternatively connecting a means for transmitting a second type of signals over said channel, means responsive to said second type of signals, a chain of switching relays responsive to said last means for controlling said first and said second connecting means, said relays being arranged to respond rapidly and certain of said relays being arranged to release slowly, and an accelerating circuit for said relays, comprising an independent energizing circuit rendered effective only during the forward movement of the armatures of said relays.

2. In a communication system, a transmission channel, means for normally connecting a means for transmitting a first type of signals over said channel, means for alternatively connecting a means for transmitting a second type of signals over said channel, means responsive to said second type of signals, a chain of switching relays responsive to said last means for controlling said first and said second connecting means, said relays including a master relay arranged to respond freely to said means responsive to said second type of signals, and a hang-over relay arranged to release slowly, and an accelerating circuit for both said relays arranged to strongly energize both said relays during the interval after said master relay has started the movement of its armature until said hangover relay has completed the movement of its armature.

3. In a communication system, a transmission channel, means for normally connecting a means for transmitting a first type of signals over said channel, means for alternatively connecting a means for transmitting a second type of signals .over said channel, means responsive to said secsnd type of signals, a chain of switching relays responsive to said last means for controlling said rst and said second connecting means, said relays including a master relay arranged to respend freely to said means responsive to said second type of signals, and a. hang-over relay arranged to release slowly, and an accelerating circuit for both said relays arranged to strongly energize both said relays during the interval after said master relayhas started the movement of its amature until said hang-over relay has completed the movement of its armature, the remainder of said chain of relays being responsive to the starting of the movement of the said armature of said hang-over relay.

4. In a communication system, a transmission channel, means for normally connecting a means for transmitting a first type of signals over said channel, means for alternatively connecting a means for transmitting a second type of signals over said channel, means responsive to Said second'type of signals, a chain of switching relays responsive to said last means for controlling said rst and said second connecting means, said relays including a master relay freely responsive to said means responsive to said second type of signals and a hang-over relay provided with a delay circuit for rendering said relay slow to release, an accelerating circuit including auX- iliary windings on said master relay and said hang-over relay and means including the armatures and contacts of said relays for controlling said accelerating circuit.

5. In a communication system, a transmission channel, means for normally transmitting telegraph signals over said channel, means for alternatively transmitting voice currents over said channel, means comprising a syllabic amplifierdetector responsive to voice currents, a chain of switching relays responsive to said syllabic amplifier-detector for switching said channel between said telegraph and said telephone means, said chain of relays including a master relay freely responsive to said syllabic amplifier-detector, a hang-over relay freely responsive to said master relay in its operation but delayed in its release, and an additional plurality of switching relays freely responsive to said hang-over relay, an accelerating circuit for said master and said hang-over relays comprising a self-controlled strongly energizing circuit responsive to the movement of the armature of said master relay from its back contact, and means responsive to the movement of the armature of said hang-over relay. from its back contact for controlling said,

additional plurality of switching relays.

6. In a communication system, a channel of 

